The present invention relates to a silver halide photographic light sensitive material spectrally sensitized in infrared region.
With recent rapid progress of information transmitting systems, silver halide photographic light sensitive materials have been increasingly required to have high sensitivity. Such systems are, for example, high speed phototypesetting system according to which information output from electronic computer is immediately displayed as letters or figures by cathode ray tube and press facsimile system for rapid transmission of news paper originals to a remote place.
Characteristics required for silver halide photographic light sensitive materials for these uses are high sensitivity to so-called high intensity-short time exposure (flash exposure), namely, exposure for 10.sup.-4 second or less with light sources, e.g., lasers such as cathode ray tube (CRT), helium-neon gas laser and light emission diode (LED), high contrast and high resolving power.
The method of using laser light sources such as helium-neon and argon as a scanning type light source has the defects that large and expensive devices are necessary and efficiency of consumed power is low. On the other hand, semiconductor laser has the advantages that it is small in size, inexpensive, easily modulatable and long in life. For semiconductor laser, there are used semiconductors of such systems as Ga/As/P; Ga/Al/As; Ga/As; In/P; In/As and the like and wavelength of these laser beams is generally longer than 700 nm and largely is longer than 750 nm.
Therefore, bright safelight can be used and thus handleability is good. However, light sensitive materials for infrared rays are generally not so high in sensitivity and inferior in shelf stability and various proposals have been made in an attempt to solve these problems. For example, a technique called supersensitization effect has been proposed according to which spectral sensitivity is markedly enhanced by adding a specifically selected organic compound in addition to spectral sensitizing dye. Reference may be made to, for example, triazine derivatives disclosed in U.S. Pat. Nos. 2,785,058 and 3,695,888, mercapto compounds having electronegative group disclosed in U.S. Pat. No. 3,457,078, benzotriazole derivatives disclosed in Japanese Patent Unexamined Publication (Kokai) No. 81613/76, quaternary salts disclosed in Japanese Patent Unexamined Publication (Kokai) No. 191032/84 and others disclosed in Japanese Patent Unexamined Publication (Kokai) Nos. 69063/86 and 27884/86. However, many of these supersensitization techniques provide unsatisfactory results such as insufficient sensitization, increase of fog and decrease in shelf stability.
As a result of the inventors' intensive research on silver halide photographic light sensitive materials for semiconductor laser beam which are free from the above mentioned problems, it has been found that some compounds are markedly effective for this purpose.